The present invention relates generally to the detection of Babesia microti infection. In particular, the invention is related to polypeptides comprising a B. microti antigen, to antigenic epitopes of such an antigen and the use of such polypeptides and antigenic epitopes for the serodiagnosis and treatment of B. microti infection.
Babesiosis is a malaria-like illness caused by the rodent parasite Babesia microti (B. microti) which is generally transmitted to humans by the same tick that is responsible for the transmission of Lyme disease and ehrlichiosis, thereby leading to the possibility of co-infection with babesiosis, Lyme disease and ehrlichiosis from a single tick bite. While the number of reported cases of B. microti infection in the United States is increasing rapidly, infection with B. microti, including co-infection with Lyme disease, often remains undetected for extended periods of time. Babesiosis is potentially fatal, particularly in the elderly and in patients with suppressed immune systems. Patients infected with both Lyme disease and babesiosis have more severe symptoms and prolonged illness compared to those with either infection alone.
The preferred treatments for Lyme disease, ehrlichiosis and babesiosis are different, with penicillins, such as doxycycline and amoxicillin, being most effective in treating Lyme disease, tetracycline being preferred for the treatment of ehrlichiosis, and anti-malarial drugs, such as quinine and clindamycin, being most effective in the treatment of babesiosis. Accurate and early diagnosis of B. microti infection is thus critical but methods currently employed for diagnosis are problematic.
All three tick-borne illnesses share the same flu-like symptoms of muscle aches, fever, headaches and fatigue, thus making clinical diagnosis difficult. Microscopic analysis of blood samples may provide false-negative results when patients are first seen in the clinic. Indirect fluorescent antibody staining methods for total immunoglobulins to B. microti may be used to diagnose babesiosis infection, but such methods are time-consuming and expensive. There thus remains a need in the art for improved methods for the detection of B. microti infection.
The present invention provides compositions and methods for the diagnosis and treatment of B. microti infection. In one aspect, polypeptides are provided comprising an immunogenic portion of a B. microti antigen, or a variant of such an antigen that differs only in conservative substitutions and/or modifications. In one embodiment, the antigen comprises an amino acid sequence encoded by a DNA sequence selected from the group consisting of (a) sequences recited in SEQ ID NO: 1-17, 37, 40, 42, 45, 50 and 51; (b) the complements of said sequences; and (c) sequences that hybridize to a sequence of (a) or (b) under moderately stringent conditions.
In another aspect, the present invention provides an antigenic epitope of a B. microti antigen comprising the amino acid sequence -X1-X2-X3-X4-X5-Ser- (SEQ ID NO: 35), wherein X1 is Glu or Gly, X2 is Ala or Thr, X3 is Gly or Val, X4 is Trp or Gly and X5 is Pro or Ser. In one embodiment of this aspect, X1 is Glu, X2 is Ala and X3 is Gly. In a second embodiment X1 is Gly, X2 is Thr and X5 is Pro. The present invention further provides polypeptides comprising at least two of the above antigenic epitopes, the epitopes being contiguous.
In yet another aspect, the present invention provides an antigenic epitope of a B. microti antigen comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 36 and 39, together with polypeptides comprising at least two such antigenic epitopes, the epitopes being contiguous.
In a related aspect, polynucleotides encoding the above polypeptides, recombinant expression vectors comprising these polynucleotides and host cells transformed or transfected with such expression vectors are also provided.
In another aspect, the present invention provides fusion proteins comprising either a first and a second inventive polypeptide, a first and a second inventive antigenic epitope, or, alternatively, an inventive polypeptide and an inventive antigenic epitope. In specific embodiments, fusion proteins comprising an amino acid sequence of SEQ ID NO: 85 or 87 are provided.
In further aspects of the subject invention, methods and diagnostic kits are provided for detecting B. microti infection in a patient. In one embodiment, the method comprises: (a) contacting a biological sample with at least one polypeptide comprising an immunogenic portion of a B. microti antigen; and (b) detecting in the sample the presence of antibodies that bind to the polypeptide, thereby detecting B. microti infection in the biological sample. In other embodiments, the methods comprise: (a) contacting a biological sample with at least one of the above polypeptides or antigenic epitopes; and (b) detecting in the sample the presence of antibodies that bind to the polypeptide or antigenic epitope. Suitable biological samples include whole blood, sputum, serum, plasma, saliva, cerebrospinal fluid and urine. The diagnostic kits comprise one or more of the above polypeptides or antigenic epitopes in combination with a detection reagent.
The present invention also provides methods for detecting B. microti infection comprising: (a) obtaining a biological sample from a patient; (b) contacting the sample with at least two oligonucleotide primers in a polymerase chain reaction, at least one of the oligonucleotide primers being specific for a DNA sequence encoding the above polypeptides; and (c) detecting in the sample a DNA sequence that amplifies in the presence of the first and second oligonucleotide primers. In one embodiment, the oligonucleotide primer comprises at least about 10 contiguous nucleotides of a DNA sequence encoding the above polypeptides.
In a further aspect, the present invention provides a method for detecting B. microti infection in a patient comprising: (a) obtaining a biological sample from the patient; (b) contacting the sample with an oligonucleotide probe specific for a DNA sequence encoding the above polypeptides; and (c) detecting in the sample a DNA sequence that hybridizes to the oligonucleotide probe. In one embodiment of this aspect, the oligonucleotide probe comprises at least about 15 contiguous nucleotides of a DNA sequence encoding the above polypeptides.
In yet another aspect, the present invention provides antibodies, both polyclonal and monoclonal, that bind to the polypeptides described above, as well as methods for their use in the detection of B. microti infection.
Within other aspects, the present invention provides pharmaceutical compositions that comprise one or more of the above polypeptides or antigenic epitopes, or a polynucleotide encoding such polypeptides, and a physiologically acceptable carrier. The invention also provides vaccines comprising one or more of the inventive polypeptides or antigenic epitopes and a non-specific immune response enhancer, together with vaccines comprising one or more polynucleotides encoding such polypeptides and a non-specific immune response enhancer.
In yet another aspect, methods are provided for inducing protective immunity in a patient, comprising administering to a patient an effective amount of one or more of the above pharmaceutical compositions or vaccines.
These and other aspects of the present invention will become apparent upon reference to the following detailed description and attached drawings. All references disclosed herein are hereby incorporated by reference in their entirety as if each was incorporated individually.